The present invention relates to hydraulic couplings. More specifically, the field of the invention is that of hydraulic port fittings such as used in automobiles, aircraft, and the like.
There are many port fittings on the marketplace currently which are designed to connect tubing or hydraulic hose to power equipment such as brake calipers etc. The most frequently used methods of attachment are the "tube-o" and the "banjo" type fittings. The former is used in brake and air conditioning systems, and the latter predominantly in brake systems.
The problem with both technologies is that they are prone to leaks which are both expensive and dangerous. Warranty and in-house costs of fixing such leaks may become quite large, and the environmental consideration of the effects of such loss of contaminating fluids cannot be ignored.
Traditionally, the hydraulics supply industry has recommended better surface finishes and tighter tolerances in manufacture in order to minimize the potential for leaks. This has, however, failed to adequately answer the problem. To adequately address this problem in the "banjo" fitting, the causes of the leaks must be examined. A description of the "banjo" port fitting is presented below which includes an examination of its inherent inadequacies.
"Banjo" fittings are so termed because of their shape, which usually comprises of a tube brazed onto a round component, giving rise to a substantially banjo-shaped assembly.
Referring to FIGS. 1 and 2, which show a prior art "banjo" fitting, a typical banjo fitting is comprised of body 102 through which bolt 103 is assembled. The combination of body 102 and bolt 103 is then assembled to port 101. Sealing of the body/bolt assembly is accomplished with copper (typically) washers 104 and 105, which are placed each side of body 102. Large torques (applied in the radial direction of arrow T of FIG. 4) are employed to obtain a seal between components, which sometimes cannot be sealed. A common failure of this assembly is to snap the bolt or strip the threads of the port while striving to attain sealing contact.
The "banjo" fittings are useful because of their inherent assembly benefits in situations where time taken to assemble and ease of access to components are important considerations. "Banjo" fittings are assembled from the front, and assembly can be effected with power tools. This is not true of other fittings which perform the function served by "banjo" fittings, that of supplying fluid to a component through a 90 degree change of direction or other similar reorientation of fluid flow.
A drawing of an assembled prior art "banjo" fitting is shown in FIGS. 1 and 2, where body 102, shown in partial cut-away, is recessed internally to create flow chamber 124 for pressurized fluid. A recessing operation is required to be done to body 102, rather than in bolt 103, in order to retain as much tensile strength in bolt 103 as possible. If bolt 103 were reduced in diameter to create a flow chamber, insufficient material would remain in bolt 103 to withstand the massive assembly torques required to obtain a seal. The recessing operation required for body 102 is expensive and difficult to control. Also, bolt 103 must be made of relatively high tensile material in order to resist tensile failure due to high torques, and such materials are hard to machine which further complicates the manufacture of prior art "banjo" fittings.
One problem with prior art "banjo" fittings involves the four potential leak-paths in any standard banjo fitting, one on each side of the metal washers 104 and 105 which are located at sealing points 120, 121, 122 and 123 of FIG. 2. Also a problem is that massive torques are required to attain a seal, which in turn, requires a high tensile strength bolt, and an internally recessed body. These are expensive requirements for the manufacture of the "banjo" fitting.
An additional problem involves the lack of any secondary seal in the port interface. Should one of the four metal-to-metal interfaces develop a leak, the only way of overcoming it is to impart greater torque to the assembly. This regularly leads to tensile failures of bolts or stripped threads on bolts or in ports.
Further problems involve shape, size and alignment of the prior art "banjo" fittings. Flow characteristics within the fitting are primarily derived from consideration of tensile strengths rather than from system demand. This often leads to flow restrictions which are not desirable. Also, the face-to-face association of components requires close control in order to form an adequate seal. Concentricity and squareness of through-bores on bodies must be carefully maintained in production, and aligned accurately during assembly, if a seal is to be obtained.
What is needed is an improved hydraulic coupling which utilizes the elastic properties of the materials from which the component parts are made.
A further need is for an improved hydraulic coupling which includes secondary seals.
An additional need exists for an improved hydraulic coupling for systems which includes metal-to-metal seals.
A still further need exists for an improved hydraulic coupling which minimizes the number of potential leak paths.
Yet another need exists for an improved hydraulic coupling which requires less torque for assembly.